For an overview see the following pictures of an analysis provided from rumpl4skn.

Note that in the pictures above the cloud fits perfect between the red an white barn. We will use them later as reference points for the diameter of the cloud. And please note that the shape of the cloud is quite sharp and clear.

...I found some more aspects to endorse the impossibility of this picture.

These are especially:

- the terrain between Val McClatchey and the "crash"-site- the diameter of the cloud,- how "old" the cloud must be,- the influence of wind and turbulences.

When we draw a profile of elevation between the "crash"-site and Val's POV then we get this:

Note that the hilltop at 1.2 miles determines her horizon. ( I ignore the trees at this point)With a little geometry we´ll find that the top(!) of the cloud has to climb at least 380ft agl to come in sight.

If we put the things together then we get the next picture:

Note that our POV is about 40ft higher than that of Vals camera.

Distance to the cloud is about 1.4 miles.View is to the west, the blue line indicates the direction of wind from NW to SE, windspeed at that day was 9-12 mph means Beaufort 3.

If we follow the horizontal angle over the red and white barn to the "crash"-site then we can calculate the diameter of the cloud to be at least 1,900 ft (indicated by the thick red horizontal line, a little bit hidden by "c")

I've put the center of the plume to an altitude 700 agl which is obviously too low. To get the complete cloud in our view it has to climb 380ft for the skyline plus 1,900 ft for the diameter = 2,280ft agl ! ("crater" is agl zero!)

The center of the clouds "chimney" is in a distance of about 970ft from the "crater" (indicated by paddle "C")

For the horizontal movement of the chimney at 9-12mph we need between 55 and 73 seconds to come in position.

For the vertical climb I tried to clock the expansion rates of the wtc2 fireball, result about 35ft/sec in the very first seconds means we need 65 seconds for Val's cloud.

A research for the climb rates of stratospheric balloons gave me values between 10 and max 50ft/sec.

So if we want to believe at this point that this mushroom cloud existed, then we have to accept that it is at least 1 minute old (the "crash" being t=0 in this example).

To be fair subtract the 8 seconds the explosion-sound needed to travel to Val. 52(!) seconds is another dimension than her claim that it had been only 5 seconds.

And the cloud is long time disconnected from the "crater"!But a strong source of energy and smoke is absolutely necessary to conserve a constant climb rate and the clear shape of the cloud.

See yourself in the videos and pictures from the WTC and the Pentagon how the smoke-plume develops ans fades!

A 21-sec video showing the shockwave and typical black smoke cloud from a detonation of 350lb of pure TNT you can see here.

Note: When the energy is gone the clear shape of the cloud fades away.

This is due to the natural turbulence of the air even at very low windspeeds.(Did you ever see snowflakes dancing in the air?)

Most people aren't aware of it but there are more than 1,000 micro-gusts per hour.

Aviation experts define turbulence as random, unpredictable motion that occurs at the boundary between layers of air moving at different speeds. Just as the smooth flow of an ocean wave breaks up into a maelstrom of swirls and eddies when it crashes on the shore, uniformly moving layers of the atmosphere that brush against each other fragment into vortices, and other small-scale disturbances.

Turbulence is often triggered when energy released by the sun-warmed ground or by a group of forming clouds heats a parcel of air at low altitude. The heated parcel rises, distorting the wind-flow pattern at higher altitudes and generating chaotic motion.

[emphasis by rSpieker]

And now consider the wind at 9/11 in Shanksville (13 to 17 ft/sec):

The following pictures from a scientific study to improve the performance of a chimney shows the influence of the wind at different speeds. Source (page 7):

Conclusion:

Apart from the fact that even if a B757 crashed near Shanksville there was simply not enough energy to produce a mushroom cloud then:

If some way a "mushroom cloud" existed in the very first seconds, there is absolute no way under the atmospheric conditions of that day to keep it stable so long that Val McClatchey's camera had a chance to "see" it.

This spells the definite "End of Serenity" for Val McClatchey's picture.